Without limiting the scope of the invention, its background is described in connection with methods and techniques for improving stability of anionic surfactants used in oil recovery.
U.S. Pat. No. 4,976,315 issued to Prukop and Chea (1990) discloses a method for increasing the recovery of oil in enhanced oil recovery operations employing anionic surfactant by blending a taurine with said anionic surfactant. The taurine may also increase the salt and divalent ion tolerance of the anionic surfactant.
Sulfonate surfactants have been the exclusive choice for high temperature application due to presumed instability of ether sulfate (ES) surfactants. As sulfonates in general are more expensive than sulfates, the costs were prohibitively high in some cases for enhanced oil recovery (EOR) to be even considered.
U.S. Pat. No. 4,331,543 issued to Wilson and Pao (1982) describes a process for the recovery of oil from subterranean oil reservoirs by waterflooding employing ether-linked sulfonate surfactants in which oxidative degradation of the surfactant is retarded through the establishment of an anaerobic condition in the surfactant solution or through the use of oxidation inhibitors. According to the '543 Patent the anaerobic condition may be provided by mechanical means such as scrubbing the injected water with an inert gas in order to remove oxygen or by employing produced well water which is handled under a closed system to exclude oxygen. A preferred class of oxidation inhibitors is sterically hindered phenolic compounds which function as free radical chain inhibitors.
U.S. Pat. No. 3,943,160 issued to Farmer et al. (1976) describes a waterflood oil recovery process, in which a mixture of petroleum sulfonate and alkoxylated alcohol sulfate surfactants is injected into a reservoir to displace oil, which is improved by using a sulfate surfactant that contains at least one chain-branching substituent on a carbon atom alpha or beta to the sulfate group. In a reservoir that is relatively hot, the improved process provides good oil-displacement efficiency and polyvalent metal ion compatibility in addition to improved stability towards hydrolytic decomposition of the sulfate surfactant.